Uninterruptible Power System 800 Guía de instalación descargar pdf (Pagina 3)

PROPERTY OF SOLIDSTATE CONTROLS, INC. 7/1998

Good data on power consumption is often hard to get for small loads such as personal computers.

Most equipment below, for example, 800 Watts, will be 120 VAC, single phase, 60 Hz. rated

(Sometimes with a dual rating for 50 Hz. And 240 VAC for overseas usage).

Usually, each component of the computer system will have a tag placed near the location the

power cord enters the device.

Underwriter’s Laboratory (UL) requires that at a minimum, the voltage, amperage, and frequency

be identified.

The arithmetic product of the voltage and the amperage, i.e., V x A, gives a result in Volt-Amperes

often stated simply, VA. The Volt-Ampere (VA) is a universally accepted measure of electrical

capacity for the UPS industry.

VA capacity simply states that a given device may draw so many amps (A) at a particular voltage

). This is often a worst case value.

Many computer manufacturers overstate their equipment capacities by 20% or so to insure that the user provides

adequate electrical service to the system.

The VA capacity tells us nothing about how efficiently the device utilizes the energy it receives. The

measure of actual electrical energy usage is the watt (W.).

Sometimes the device label will state a wattage value, and this is particularly true for small loads

below 800 watts. Many small UPS systems will have their capacity stated in watts rather than volt-

amperes.

The ratio of watts over VA, i.e., W + VA gives us a measure of power utilization called the power

factor (p.f.).

For example, a computer with a volt-ampere rating of 120 VA, and a wattage rating of 96 watts has

a power factor of 0.8.

96 watts = 0.8 p.f.

120 VA

A good rule of thumb is to assume a power factor of 0.8 if both the wattage and volt-ampere rating

are not known.

For example, an IBM desktop computer, the PS/2 Model 30 has the following label attached in the

back:

100-125 VAC 100-125 VAC

1.5 A .9 A

50/60 Hz. 60 Hz.

1 2 3 4 5 6 7 8 ... 23 24

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Uninterruptible Power System 800 Guía de instalación Pagina 3